Conventionally, Bluetooth (registered trademark) and ad-hoc mode of a wireless LAN are known as so-called Device-to-Device (D2D) communication that is a radio communication method in which multiple radio communication terminals (sometimes referred to simply as terminals hereinbelow) perform radio communication with each other directly without involving a radio base station or an access point. Such a radio method achieves short-range radio communication by using relatively-low radio transmission power. For this reason, it is difficult to use this radio communication method when the inter-terminal distance is long.
Against this background, it is being discussed to achieve the D2D communication by using a radio access network (e.g., UTRA (3G), E-UTRA (LTE), or GERAN (2G)) provided by a telecommunications carrier (e.g., Non-patent document 1).
In the case of using such radio access technology, the terminals use a frequency band which the telecommunications carrier is licensed to use by supervisory authorities, and therefore are enabled to output higher radio transmission power and achieve long-distance D2D communication without using resources on the network side such as a radio base station. Such a characteristic is considered particularly effective when the network side such as the radio base station is devastated by an earthquake or the like. Further, when the D2D communication is achieved using the frequency band used in a radio access network (such as 2G, 3G, or LTE) managed by a telecommunications carrier, the terminals can perform the D2D communication without being equipped with a module for another type of radio communication (e.g., Bluetooth (registered trademark)), which offers advantages such as cost and size reductions for the terminals.